System and method for vibrating screens to reduce speckle

ABSTRACT

The present disclosure includes systems and methods for solving speckle problems by exciting the screen with a more complex vibration spectrum. A range of frequencies provides, in effect, a collection of overlapping patterns of high and low displacement, so that all regions of the screen have enough motion to reduce visible speckle. As previously discussed acceptable speckle may be approximately 15% contrast or less, preferably approximately 5% contrast or less at approximately 15 feet from the screen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent App. No.61/832,047, entitled “Screen vibration for reducing speckle”, filed 6Jun. 2013 (RealD Ref: 363000), the entirety of which is hereinincorporated by reference.

TECHNICAL FIELD

This disclosure generally relates to systems and methods for reducingspeckle in engineered screens using screen vibration.

BACKGROUND

The use of coherent or partially coherent light sources can haveadvantages in display or illumination over standard incoherent sources(lamps), in that they can achieve higher brightness, better reliability,and larger color gamut. However, with this increased coherence comes theissue of speckle interference. Speckle is due to interference of thelight reflecting from the screen or target that causes variations inintensity that can be seen by the observer or instrument. High spatialfrequency, intensity variations are typical and very undesirable fordisplay or imaging applications.

BRIEF SUMMARY

According to an aspect of the present disclosure, a method for reducingspeckle on a projection screen may include vibrating a projection screenwithin a predetermined frequency spectrum, in which the predeterminedfrequency spectrum has power which is broadly dispersed within thepredetermined frequency spectrum. As a result, speckle may be mitigatedon the projection screen to within an acceptable level. The projectionscreen may be vibrated with at least one primary transducer which maybe, for example, a voice coil. The predetermined frequency spectrumpower may be primarily in the approximate range of 30-500 Hertz. Theacceptable level for speckle may be less than approximately 15 percentcontrast at approximately fifteen feet from the projection screen. Theprojection screen may include a high elastic modulus substrate, with anelastic modulus of greater than approximately 0.4 GPa. The vibratingelement may be directly attached to the projection screen oralternatively the vibrating element may be mounting to a mounting patchwhich may be attached to the projection screen. The method may alsoinclude producing an acceptable level of audible noise which may be lessthan approximately 40 dBm.

Continuing the discussion, the method may include detecting primarytransducer failure by measuring the projection screen vibrations. Thescreen vibrations may be measured with at least one accelerometer.Redundant transducers may also be located on the projection screen inaddition to the primary transducers. The redundant transducers may bedriven only when a failure of at least one primary transducer isdetected. The primary and redundant transducers may be located behindmasking to reduce acoustic transmission from the transducers.

In another aspect of the present disclosure, a projection screen systemmay include a projection screen and at least one primary vibratingelement attached to the projection screen, in which the vibratingelement vibrates the screen within a predetermined frequency spectrum.The predetermined frequency spectrum may have power which is broadlydispersed within the predetermined frequency spectrum. Also, vibratingthe projection screen may mitigate speckle to an acceptable level. Theprojection screen may include a high elastic modulus substrate with anelastic modulus of greater than approximately 0.4 GPa. The at least oneprimary vibrating element may be at least one transducer, which may be avoice coil. The predetermined frequency spectrum may be in theapproximate range of 50-200 Hz. The acceptable level for speckle may beless than approximately 15 percent contrast at approximately fifteenfeet from the projection screen. The at least one primary vibratingelement may be mounted directly adjacent to the projection screen.

Continuing the discussion, the projection screen system may includeredundant vibrating elements in addition to the at least one primaryvibrating element. The redundant vibrating elements may be driven onlywhen a failure of at least one of the primary vibrating elements isdetected. Masking may be located to dampen audible acoustic transmissionfrom the at least one primary vibrating element. The masking may belocated on the front and the back of the projection screen and maycomprise absorbing material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example in the accompanyingFIGURES, in which like reference numbers indicate similar parts, and inwhich:

FIG. 1 is a schematic diagram illustrating a screen system used forreducing speckle, in accordance with the present disclosure;

FIG. 2 is a schematic diagram illustrating another screen system forreducing speckle, in accordance with the present disclosure;

FIG. 3 is an illustration of a mechanical transducer mounted on amounting strip, in accordance with the present disclosure;

FIG. 4 is a schematic diagram illustrating a spectrum of screenvibration using a mechanical transducer, in accordance with anembodiment of the present disclosure;

FIG. 5 is schematic diagram illustrating a power spectrum of a noisesource tailored to have both low and high frequencies diminished, inaccordance with the present disclosure;

FIG. 6 is an illustration of a voice coil transducer, in accordance withthe present disclosure; and

FIGS. 7A and 7B are illustrations of a voice coil and a mount, inaccordance with the present disclosure.

DETAILED DESCRIPTION

According to an aspect of the present disclosure, a method for reducingspeckle on a projection screen may include vibrating a projection screenwithin a predetermined frequency spectrum, in which the predeterminedfrequency spectrum has power which is broadly dispersed within thepredetermined frequency spectrum. As a result, speckle may be mitigatedon the projection screen to within an acceptable level. The projectionscreen may be vibrated with at least one primary transducer which may bea voice coil. The predetermined frequency spectrum power may beprimarily in the approximate range of 30-500 Hertz. The acceptable levelfor speckle may be less than approximately 15 percent contrast atapproximately fifteen feet from the projection screen. The projectionscreen may include a high elastic modulus substrate, with an elasticmodulus of greater than approximately 0.4 GPa. The vibrating element maybe directly attached to the projection screen or alternatively thevibrating element may be mounting to a mounting patch which may beattached to the projection screen. The method may also include producingan acceptable level of audible noise which may be less thanapproximately 40 dBm.

Continuing the discussion, the method may include detecting primarytransducer failure by measuring the projection screen vibrations. Thescreen vibrations may be measured with at least one accelerometer.Redundant transducers may also be located on the projection screen inaddition to the primary transducers. The redundant transducers may bedriven only when a failure of at least one primary transducer isdetected. The primary and redundant transducers may be located behindmasking to reduce acoustic transmission from the transducers.

In another aspect of the present disclosure, a projection screen systemmay include a projection screen and at least one primary vibratingelement attached to the projection screen, in which the vibratingelement vibrates the screen within a predetermined frequency spectrum.The predetermined frequency spectrum may have power which is broadlydispersed within the predetermined frequency spectrum. Also, vibratingthe projection screen may mitigate speckle to an acceptable level. Theprojection screen may include a high elastic modulus substrate with anelastic modulus of greater than approximately 0.4 GPa. The at least oneprimary vibrating element may be at least one transducer, which may be avoice coil. The predetermined frequency spectrum may be in theapproximate range of 50-200 Hz. The acceptable level for speckle may beless than approximately 15 percent contrast at approximately fifteenfeet from the projection screen. The at least one primary vibratingelement may be mounted directly adjacent to the projection screen.

Continuing the discussion, the projection screen system may includeredundant vibrating elements in addition to the at least one primaryvibrating element. The redundant vibrating elements may be driven onlywhen a failure of at least one of the primary vibrating elements isdetected. Masking may be located to dampen audible acoustic transmissionfrom the at least one primary vibrating element. The masking may belocated on the front and the back of the projection screen and maycomprise absorbing material.

Although the problem of speckle interference or speckle is a knownproblem, only a number of partial solutions exist. The measurement andcharacterization of speckle is also known. Speckle is measured bymeasuring the contrast of the light intensity and may be defined as thestandard deviation over the mean of the intensity. An explanation of howto measure speckle see reference by Jacques Gollier of Corning, Inc.from the conference “Projector Summit 2010”, Las Vegas Nev., May 7, 2010entitled “Speckle Measurement Procedure.”

Various methods attempting to reduce the visibility of speckle will bediscussed below.

One family of solutions utilizes moving one or more diffusers to achievechanges to the local optical phase to temporally average out some of thespeckle over the observer's/detector's integration period. This isgenerally discussed in U.S. Pat. No. 5,313,479, “Speckle-free displaysystem using coherent light,” and U.S. Pat. No. 7,585,078, “Illuminationsystem capable of eliminating laser speckle and projection systememploying the same.” The diffusers can also vibrate with a large enoughamplitude to cover several diffractive elements to achieve someaveraging as well. This is generally discussed in U.S. Pat. No.7,922,333, “Projector, screen, projector system, and scintillationremoving apparatus for removing scintillation on an image.”

Another family of solutions to reduce speckle uses moving mirrors orphase modulators to achieve the temporal averaging. This is generallydiscussed in U.S. Patent Pub. No. 2011/0102748, “Optical system andmethod,” U.S. Patent Pub. No. 2010/0053476, “Systems and methods fordespeckling a laser light source,” U.S. Pat. No. 4,155,630, “Speckleelimination by random spatial phase modulation,” and U.S. Pat. No.7,489,714, “Speckle reduction laser and laser display apparatus havingthe same.” These use expensive moving parts or phase modulators.

Another solution uses a large core, long, very high numerical aperture(NA) multimode fiber to “decoher” a laser beam. This is generallydiscussed in U.S. Patent Pub. No. 2009/0168025, “Decohered laser lightproduction system.” This system discusses the use of a 12 mm diametercore fiber with an NA of 0.65. This large fiber may provide somereduction in speckle, but destroys the brightness of the system sincethe etendue is so large. Although there may be some benefits to using avery long multimode fiber, as generally discussed in U.S. Patent Pub.No. 2010/0079848, “Speckle reduction in display systems that employcoherent light sources,” the use of such a long multimode fiber reducesthe power with absorption. Multimode fiber speckle issues and solutionsare discussed further in the book SPECKLE PHENOMENA IN OPTICS by JosephGoodman (Roberts and Company, 2006, Chapter 7).

A family of solutions has been proposed that divide the laser beams upinto parts and then force each part to have a different path length, orchange of polarization, before recombining the beams. The use of fiberbundles or splitter/combiners or lens-let arrays may be generallydiscussed in U.S. Patent Pub. No. 2005/0008290 “Static method for laserspeckle reduction and apparatus for reducing speckle,” U.S. Pat. No.4,360,372, “Fiber optic element for reducing speckle noise,” U.S. Pat.No. 6,895,149, “Apparatus for beam homogenization and specklereduction,” U.S. Pat. No. 7,379,651, “Method and apparatus for reducinglaser speckle,” U.S. Pat. No. 7,527,384, “Illumination system toeliminate laser speckle and projection system employing the same,” andU.S. Pat. No. 7,719,738, “Method and apparatus for reducing laserspeckle.” These methods use expensive fiber bundles or lens arrays ormany fiber coupler/splitters to achieve some reduction in speckle.

Another family of solutions utilizes sources with larger opticalspectral bandwidths. This can be achieved by chirping the drive current,using several lasers of different wavelengths, or other means. This mayrequire additional expense or loss of light in the projection system.

Mechanical translation or rotation of screens is another approach formitigating speckle. In the book, SPECKLE PHENOMENA IN OPTICS by JosephGoodman (Roberts and Company, 2006, Chapter 6), Goodman calculates theneeded linear shift rate of the screen in x or y or screen rotation.These motions are in the plane of the screen which is roughly normal tothe projection direction needed to average out some of the speckleduring the observer's/detector's time integration period. By moving thescreen, the light sequentially hits different parts of the screen, whichthen changes the speckle pattern. If this is done fast relative to thedetector's integration period (for example, the eye is roughly 20 Hz)then the detector will see an average of several speckle patterns whichresults in a lower speckle contrast. U.S. Pat. No. 5,272,473,“Reduced-speckle display system,” discloses the use of a transducerattached directly to the screen to mechanically generate surfaceacoustic waves to minimize speckle. U.S. Pat. No. 6,122,023,“Non-speckle liquid crystal projection display” uses a highly scatteringliquid crystal as a screen and then electrically changes the liquidcrystal states to alleviate speckle. Additional solutions use scatteringliquids or diffuser cells as screens to improve speckle as generallydiscussed in U.S. Pat. No. 6,844,970, “Projection television set,screens, and method,” U.S. Pat. No. 7,199,933, “Image projection screenwith reduced speckle noise,” U.S. Pat. No. 7,244,028, “Laser illuminatedprojection displays,” U.S. Pat. No. 7,342,719, “Projection screen withreduced speckle,” and U.S. Patent Pub. No. 2010/0118397, “Reduced laserspeckle projection screen.”

In practice, a few of the above-described techniques may be usedtogether to mitigate speckle effects. However, all of the aforementionedapproaches involve using additional parts and/or physical translation toachieve speckle reduction. These additional parts increase cost,decrease brightness, and reduce reliability.

The present disclosure uses screen vibration to reduce speckle indisplay and projection applications. Typically, movie screens are madeof a polymer substrate, usually elastic polyvinylchloride (PVC) rollstock that is perforated for acoustic transmission and then seamedtogether to make a screen of the desired size. These conventionalscreens are typically 0.2-0.6 mm thick, elastic with a low Young'smodulus (elastic modulus), heavily plasticized, and embossed with amatte texture. To produce a polarization preserving screen, this elasticPVC screen is then sprayed with a polarization preserving coating. Theconventional coating generally employs a type of metal flake, forexample, ball-milled aluminum powder, encased in a polymer binder. Theseconventional screens are relatively heavy, elastic, and have a lowYoung's modulus, typically in the range of 40-60 MPa.

Significant optical performance improvements can be realized byutilizing an engineered screen with a metalized embossed surface, asdescribed in U.S. Pat. No. 8,072,681, which is herein incorporated byreference in its entirety. For proper fidelity in the engineered screen,a more rigid substrate, such as polyester, PCT or polycarbonate (PC),may be used. Appropriate substrates may include high elastic modulus(Young's modulus) substrates that are in the approximate range of 0.4Gpa-6 Gpa, preferably above 1 Gpa. Additionally, a hybrid approach mayuse the embossed surface of an engineered screen to form a texturedmetal flake, as described in the commonly owned U.S. Pat. No. 8,169,699,entitled “Polarization preserving projection screen with engineeredpigment and method for making same,” or to physically chop the metalizedsubstrate, as described in commonly owned U.S. Pat. No. 8,194,315,entitled “Polarization preserving projection screen with engineeredparticle and method for making same,” both herein incorporated byreference in their entirety and either of which could then be utilizedto replace the metal flake in a conventional screen system. The systemsand methods described in the present application may further be employedadvantageously in other commonly owned projection screen applications,including but not limited to described in the commonly owned U.S. Pat.No. 7,898,734, entitled “Polarization preserving front projectionscreen,” U.S. Pat. No. 8,072,681, entitled “Polarization preservingfront projection screen material,” U.S. Pat. No. 8,004,758, entitled“Polarization preserving front projection screen microstructures,” andU.S. Pat. No. 8,711,477, entitled “Polarization preserving frontprojection screen microstructures,” all of which are herein incorporatedby reference in their entirety.

The substrates of these engineered screens, and, therefore, theengineered screens, are much lighter and have a higher Young's modulusthan conventional elastic PVC screens. The engineered screen substratesmay be any appropriate high elastic modulus substrate such as PC, PET,rigid PVC, cycloolefins, and so forth. Rear-projection polarizationpreserving screens typically employ a diffusely scattering transparentpolymer substrate, an embossed transparent substrate, or a combinationof the two.

Accordingly, in the aforementioned new engineered screens with highelastic modulus substrates, vibrations resulting from a higher frequencyrange can travel further than in traditional screens with low elasticmodulus substrates. The higher modulus allows for surface waves with alarger out of screen plane component to be generated and propagatedsignificantly further across the screen. This out of screen plane waveis much more effective at reducing speckle than moving the screen inplane. Additionally, both a broad frequency spectrum and a highfrequency spectrum do not propagate effectively across the traditionalscreens. As a result, lower frequencies have to be applied to thetraditional screens for effective propagation through the screensubstrate, which result in audible noise. Further, to reduce speckle ontraditional screens with the standard vinyl or elastic PVC substratesystems employ a frequency in the approximate range of 20-30 Hz ashigher frequencies do not propagate effectively in these substrates orany low elastic modulus substrate. This is particularly true for screensizes used in cinema applications which are typically larger than 10feet in width.

Moreover, higher frequencies can be used to excite the screen since theypropagate more efficiently across these engineered screens. As disclosedherein, frequencies in the range of 30-500 Hz can be used, preferably inthe approximate range of 50-200 Hz. In certain embodiments the frequencyrange may be in the range of 40-300 Hz. These frequencies induce motionin the screen that is harder to see than lower frequency ranges, andbetter average the speckle patterns than lower frequency ranges,resulting in more effective mitigation of speckle visibility. Acceptablespeckle may be approximately 15% or less contrast at approximately 15feet from the screen, preferably approximately 5% or less contrast. Inaddition, the disclosed systems and methods do not require a transducerto be attached to or in contact with the portion of the screen where theimage is displayed, as further described in reference to FIG. 1. Stateddifferently, the transducers may be attached to the edge portion of thescreens or the area of the screen that may be masked from viewing. Thetransducers may not be attached to the front or back of the screen areathat is within the viewing area or the area that is not masked. This isadvantageous as locating transducers in the viewing area on either orboth of the front or back of the screen may result in a higherlikelihood of visibility. Additionally, should the transducers belocated in the viewing area on either or both of the front or back ofthe screen, the vibrations may be visible to the audience which isundesirable as it is distracting and detracts from image quality andviewing enjoyment.

Additionally, mechanical excitation of a screen with good propagationcharacteristics can give rise to standing waves, with their associated“nodes” of little or no displacement. These regions of low displacementshow visible speckle, and these regions of speckle may manifest in apattern that depends on the details of the wave propagation across thescreen. Small differences in seam structure, or attachment mechanics,appear to lead to a complex standing wave pattern.

In addition, screen vibration can cause audible noise. Vibrations thatare close to single frequencies or harmonics of near single frequenciescause noise that is very distinct and easy to hear. Acceptable audiblenoise may be approximately 40 dBm or less, preferably approximately 35dBm or less at approximately 15 feet from the screen.

The present disclosure includes systems and methods for solving theseproblems by exciting the screen with a more complex vibration spectrum.A range of frequencies provides, in effect, a collection of overlappingpatterns of high and low displacement, so that all regions of the screenhave enough motion to reduce visible speckle. As previously discussedacceptable speckle may be approximately 15% contrast or less, preferablyapproximately 5% contrast or less.

Further, the disclosure includes systems and methods for determining therange of frequencies which may be effective in removing visible specklewithout causing excessive audible sound. In one embodiment, the initialspectrum may be a broad spectrum of “white” or “pink” noise or othercomplex broadband waveforms. The broad spectrum may then be adjustedwith high and/or low pass filters in software and/or hardware whilemonitoring the response of the screen. In an exemplary embodiment, thenoise source may be from analog electronics or may be a pseudo-randomnoise stream from a computer program.

In an alternative embodiment, the screen edges may be mounted to absorbsome of the vibrational energy in the screen. According to thisembodiment, the screen termination can be damped to attenuatereflections of travelling waves from the edge of the screen and also tominimize standing waves or regions of interference in vibration.Elastomeric bands or damped springs, rather than simple springs, may beused as mounting hardware. Alternatively, energy absorbing structures,such as foam rubber pieces, can be incorporated into the mountinghardware.

FIG. 1 is a schematic diagram illustrating a screen system for reducingspeckle. The screen 100 may include one or more mounting strips 102. Themounting strips 102 add stiffness and thickness to the screen 100, andmay spread the load from mounting holes 106 in the edge of the screen100. In an embodiment, there may be mounting strips 102 on the top ofthe screen 100 and on the bottom of the screen 100. In alternativeembodiments, there may be a mounting strip 102 only on the top of thescreen 100, or only on the bottom of the screen 100. In yet anotherembodiment, the mounting strip may be cut into smaller patches, forexample, approximately four inch mounting patches, and may be locatedacross the top and the bottom of the screen. Additionally, mountingpatches can be smaller than approximately one inch or as large asapproximately fifteen inches wide. These methods are generally discussedin Provisional Patent App. No. 61/938,304, “Strain relieved mountingmethod for screen material,” filed Feb. 11, 2014, and which is hereinincorporated by reference in its entirety.

Mounting holes 106, which may be grommeted, allow mounting springs orcords to be attached to the screen 100, and then to the screen mountingframe, to tension and mount the screen 100 in a convenient way. Mountingstrips on the sides of the screen maybe used as well, as described inthe commonly-owned U.S. App. No. 61/697,692, entitled “Mechanical designand optical benefits of high elastic modulus cinema screen substrates,”which is herein incorporated by reference in its entirety.

The screen 100 also includes one or more transducers 104 mounted on themounting strips 102. In one embodiment, this may increase the range thatthe vibrations travel across the screen 100. In another embodiment andas will be discussed with respect to FIG. 2, the transducers may also beattached directly to the screen edges as opposed to mounting thetransducers to the mounting strip or mounting patches.

Continuing the discussion of FIG. 1, the vibrations can travel farenough across the screen such that the transducers 104 can be attachedin various configurations around the edges of the screen 100.Significantly, the transducers 104 do not have to be attached to or incontact with the front or the back of the screen 100 are in which theimage is displayed. Stated differently, the transducers may be mountedon the edges of the screens or in the screen area that is masked.Placing the transducers behind the screen masking is also beneficial fornoise reduction. Typical masking may range from approximately 1 inch toa couple of feet depending on the screen mounting scheme, room and imagegeometry. The masking is typically black and can be complemented withnoise absorbing or reflecting materials such as plastics, foam, fabrics,wool, metal, wood, or any other appropriate material, or any combinationthereof. Masking may be located or hung in front of the screen edge oredges with a wire or cord stretched in front of the screen portion to bemasked and attached to the screen frame. In order to position themasking closer in proximity to the screen without touching the screen, ametal bar or metal sheet may be used to hold the sound absorbing maskingcloser to the screen. The masking may be located across the whole screenperimeter or edges or only at the transducer locations. For soundreduction reasons, masking on the front and back of the screen may beused.

For smaller screens, one or more vibration transducers 104 may bemounted at the bottom of the screen 100. The transducers 104 can bemounted using screws and plates that clamp the mounting strip 102 andhold the transducers 104 to the screen 100. Another alternative is tohave the transducers 104 mounted to the metal frame of the screen 100and in contact with the mounting strip 102. Typically, the spacing canbe from 4 to 40 feet apart on the mounting strip 102. Because themounting strip 102 is mechanically more robust, heavy transducers and/ormore forceful transducers can be used. The mounting strip 102 may alsomore uniformly couple the vibration to the screen 100 over an area,rather than as a point contact. Mounting transducers by gluing them tothe mounting strip (with or without additional plates) is also possible.Ideally the mass of the mounting hardware may be minimized so that thevibration is not dampened. Mounting the vibrating elements ortransducers to patches or directly to screen with these methods is alsopossible depending on the weight of the transducers. The terms vibratingelements and transducers may be used interchangeably herein for purposesof discussion only and not of limitation.

Transducers 104 may include mechanical elements or devices such asmechanical vibration devices, off-axis or unbalanced motors, flexures orregular motors (either linear motion or rotary), piezo-electric, voicecoils, or other types of vibration devices. However, where spinningmotors are used, the resulting excitations are single-frequencydominated or harmonic dominated. Vibrations that are close to singlefrequencies or harmonics of near-single frequencies cause noise that canbe more distinct and easy to hear as previously discussed.

FIG. 2 is a schematic diagram illustrating another screen system forreducing speckle. The screen system of FIG. 2 is similar to the screensystem of FIG. 1, however, FIG. 2 does not include a mounting strip. Thescreen 200 may include one or more mounting patches 202. The mountingpatches 202 may include eye loops for attaching the screen to a frame.The screen 200 may be attached with shock cords, springs, or any otherappropriate element. Also illustrated in FIG. 2 are the transducers 210.The transducers 210 may be mounted on a mounting patch 202, mountingstrip (not shown), or mounted directly on the screen 200 as shown inFIG. 2. The transducers 210 may have spacing 220. The transducer spacingmay be determined by the size and the elastic modulus of the screensubstrate. The transducer spacing may additionally be determined by theenergy/power of signal input into the transducer and transferred to thescreen for acceptable speckle reduction. The practical energy/power thatcan be used may be limited by transducer characteristics such asreliability, power handing capabilities, and so forth, and the audiblenoise that may be generated. In general, more transducers with lesspower may be spaced apart and may result in quieter operation than onevery powerful transducer, and may result in better speckle suppression.

FIG. 3 is an illustration of a mechanical transducer 104 mounted on amounting strip 102. The illustration of FIG. 3 also includes bands 108that tension the screen 100. In an embodiment, the screen terminationcan be damped to attenuate reflections of travelling waves from the edgeof the screen 100 as well as reducing the formation of standing waveseven for more limited bandwidth vibrations. Thus, elastomeric bands 108or damped springs, rather than simple springs, may be used as mountinghardware, as shown in FIG. 3. Alternatively, energy absorbingstructures, such as foam rubber pieces, can be incorporated into themounting hardware. In addition, the mounting hardware may be configuredsuch that the vibration does not generate additional audible noise. Thuscords or damped springs may function better than typical metal springsfor acoustic purposes.

FIG. 4 is a schematic diagram illustrating a spectrum 400 of screenvibration using a mechanical transducer. FIG. 4 illustrates frequenciesgenerated on an engineered screen with high elastic modulus. Themechanical transducer used to generate the spectrum 400, producedharmonics which are audible and above an acceptable noise level. Stateddifferently, the power or energy of the mechanical transducer isconcentrated at harmonic frequencies and produces undesirable audiblenoise. More specifically, the human brain recognizes and/or hears tonesor concentrated harmonic frequencies very well, as compared to not beingable to easily recognize or hear an approximately equal amount of andwidely dispersed amount of power spread across many frequencies.

FIG. 5 is schematic diagram illustrating a power spectrum 500 of a noisesource tailored to have both low and high frequencies diminished. FIG. 5illustrates Hertz on the x-axis and normalized power/Hertz on they-axis. The spectrum 500 is a predetermined frequency spectrum or powerspectrum of the electrical signal that drives the transducers. Stateddifferently, the spectrum 500 is the Fourier transform of the electricalsignal provided to the transducer. Generally, higher frequencies areeasier to hear and therefore undesirable and lower frequencies are hardto excite well without large, heavy transducers, such as sub woofers ascompared to normal speakers, and can cause beating effects with certainprojector flash frequencies. This power spectrum may be generated byemploying high band pass and low band pass filters to filter white noiseor other broadband waveforms to produce the spectrum of FIG. 5.

Further, FIG. 5 illustrates power or energy that is broadly dispersedwithin the predetermined frequency spectrum, as opposed to FIG. 4 whichillustrates power or energy concentrated at harmonic frequencies andpower or energy that is not broadly dispersed within the frequencyspectrum. As shown in FIG. 5, some frequencies have higher energy inthis waveform but in general the waveform of the vibration or signal isspread or broadly dispersed across many frequencies. The amount ofenergy in a specific frequency is typically not of primary importance.The signal can be tailored to the transfer function of the transducerfor best operation of speckle reduction, minimal sound, and best powerefficiency. The predetermined frequency spectrum may be in theapproximate range of 30-500 Hz, and preferably in the approximate rangeof 50-200 Hz. In certain embodiments the predetermined frequency rangemay be in the range of 40-300 Hz.

A noise source can be tailored to a predetermined frequency spectrum orpower spectrum and may have both high and low frequencies diminished toreduce the visibility of speckle over the whole screen area withoutcausing objectionable audible noise. An exemplary spectrum 500, such asthe one depicted in FIG. 5, may be used to drive a transducer ortransducers 104 attached to a screen 100, which reduces the visibilityof speckle over the whole screen area without causing objectionableaudible noise. Lightweight plates that clamp the screen 100 on bothsides can be used to effectively couple the voice coil transducer 104 tothe screen directly as described in FIG. 2, or the screen mounting stripas described in FIG. 1. In an alternative embodiment, piezoelectricdevices can be driven with complex waveforms. A range of frequenciesprovides, in effect, a collection of overlapping patterns of high andlow displacement, so that all regions of the screen 100 have enoughmotion to reduce visible speckle.

The motion induced by the transducers may be in the z-direction or outof the screen plane. This may better mitigate speckle than motion in thescreen plane, by time averaging multiple speckle patterns during theintegration time of the eye. The integration time of the eye istypically in the approximate range of 50 milliseconds-150 milliseconds.Multiple transducers can be mounted together and may be driven by thesame electronics. The multiple transducers may be located on differentsides of the screen or the same side of the screen. The relative phasesof the transducers can be in or out of phase or randomly phased. Extraor redundant transducers can be placed on the screen in addition to theprimary vibrating elements or primary transducers. The redundanttransducers or redundant vibrating elements may only be employed ordriven when a failure of another primary transducer is detected toincrease reliability of the system. The primary transducers may be thetransducers that are driven in the normal state of the projection screensystem, whereas the redundant transducers may only be driven when aprimary transducer fails. Failures can be detected by measurement ofscreen vibration with accelerometers or measured when a particularprimary transducer is open or shorted. Additionally, in the case thatone or more redundant transducers are vibrating the screen, theseredundant transducers may be monitored for failure as well. Should oneof the redundant transducers fail, then another redundant transducer maybe employed to vibrate the screen.

Further, the disclosure provides methods for determining the approximaterange of frequencies that may be effective in removing visible specklewithout causing excessive audible sound. One way of accomplishing thisis to start with broad spectrum “white” or “pink” noise and then adjusthigh and low pass filters in software or hardware while monitoring theresponse of the screen. The noise source may be from analog electronicsor may be a pseudo-random noise stream from a computer program.According to an exemplary method, a noise stream can be created in acomputer program and then the acoustic filter values can be varied untila satisfactory result is achieved, such as generating noise less thanapproximately 40 dBm. An exemplary noise spectrum is white noise that ishigh-pass filtered with roll-off of 24 dB per octave with a −3 dBfrequency of 30 Hz and a low-pass filter with a roll-off of 24 dB peroctave and a −3 dB frequency of 70 Hz. The noise or frequency spectrummay vary based on the type of transducer, the screen substrate, thestrip substrate, and whether the transducer is mounted directly to thescreen or mounted on a patch that is attached to the screen.

FIG. 6 is an illustration of a voice coil transducer 604 attached to thescreen 100 of FIG. 1. As shown in FIG. 6, lightweight plates that clampthe screen 100 from both sides can be used to effectively couple thetransducer 604 to the screen mounting strip 102 or directly to thescreen as discussed with respect to FIG. 1. As previously discussed thelightweight plate that clamps the transducer to the screen may propagateless audible noise when compared to heavier clamping mechanisms that maybe employed. The lightweight plates may weigh less than approximately150 grams and preferably less than approximately 50 grams.

FIGS. 7A and 7B are illustrations of a voice coil 710 and a mount 720.Transducers, such as the voice coil illustrated in FIGS. 7A and 7B canbe mounted to the screen in a number of ways. The transducerse orvibrating elements can be mounted on a mounting strip, a patch, ordirectly to the screen. The mounting strip may be a strip that is gluedto one or both sides of the edge of the screen to make the attachmentarea for mounting the screen to the screen frame thicker, as previouslydiscussed. A patch may be a plastic patch that may be mounted to thescreen, by glue or mechanical means and contains a method for hookingthe screen to a spring, shock cord, cord or other device to connectscreen to the frame. A patch used to mount a transducer may not employ amethod to connect to a shock cord or other device. The transducer can bemounted to these areas by mechanical means such as being glued or theuse of bolts and screws through the screen, however, these methodstypical damage the screen.

In FIGS. 7B and 7B an alternative family of mounting solutions ispresented. A mechanical mount can hold the transducer so that the twohalves of the mount clamp or press the screen from both sides. FIG. 7Aillustrates a picture of the transducer which is a voice coil 710 and aclamping mount 720. As shown in FIGS. 7A and 7B, it is made of plasticbut other materials can be used; however, light materials are typicallybetter. Additionally illustrated in FIG. 7B, is the voice coil insertedinto the mount with the mount clamp closed by using two screws, bolts,nuts, or any other appropriate fastening element. The bolts or screwsmay pass through the screen so that the assembly can be located on anypart of the screen perimeter or edges. With that said, the assembly mayalso be placed at the edge of the screen but with the bolts located offthe screen so that no holes are needed in the screen. In this example,the rest of the mount may still clamp the screen to hold the transducerto the screen, but without damaging the screen. This may allow thetransducers to be placed anywhere on the edge perimeter of the screen.Multiple transducers can be placed around the screen depending on thesize of the screen and for redundancy should any fail.

As may be used herein, the terms “substantially” and “approximately”provide an industry-accepted tolerance for its corresponding term and/orrelativity between items. Such an industry-accepted tolerance rangesfrom zero percent to ten percent and corresponds to, but is not limitedto, component values, angles, et cetera. Such relativity between itemsranges between approximately zero percent to ten percent.

While various embodiments in accordance with the principles disclosedherein have been described above, it should be understood that they havebeen presented by way of example only, and not limitation. Thus, thebreadth and scope of this disclosure should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with any claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theembodiment(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” the claims should not be limited by the languagechosen under this heading to describe the so-called field. Further, adescription of a technology in the “Background” is not to be construedas an admission that certain technology is prior art to anyembodiment(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the embodiment(s) set forth inissued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple embodimentsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theembodiment(s), and their equivalents, that are protected thereby. In allinstances, the scope of such claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

1. A method for reducing speckle on a projection screen, comprising:vibrating a projection screen within a predetermined frequency spectrum,wherein the predetermined frequency spectrum has power which is broadlydispersed within the predetermined frequency spectrum; and mitigatingspeckle on the projection screen to an acceptable level.
 2. The methodfor reducing speckle on a projection screen of claim 1, furthercomprising vibrating the projection screen with at least one primarytransducer.
 3. The method for reducing speckle on a projection screen ofclaim 2, wherein the at least one primary transducer further comprises avoice coil.
 4. The method for reducing speckle on a projection screen ofclaim 1, wherein the predetermined frequency spectrum power is primarilyin the approximate range of 30-500 Hertz.
 5. The method for reducingspeckle on a projection screen of claim 1, wherein the acceptable levelfor speckle is less than approximately 15 percent contrast atapproximately fifteen feet from the projection screen.
 6. The method forreducing speckle on a projection screen of claim 1, wherein theprojection screen further comprises a high elastic modulus substrate. 7.The method for reducing speckle on a projection screen of claim 6,wherein the high elastic modulus substrate has an elastic modulus ofgreater than approximately 0.4 GPa.
 8. The method for reducing speckleon a projection screen of claim 1, further comprising attaching at leastone vibrating element directly to the projection screen.
 9. The methodfor reducing speckle on a projection screen of claim 1, whereinvibrating the screen further comprises producing an acceptable level ofaudible noise of less than approximately 40 dBm.
 10. The method forreducing speckle on a projection screen of claim 2, further comprisingmounting the at least one primary transducer to a mounting patch,wherein the mounting patch is attached to the projection screen.
 11. Themethod for reducing speckle on a projection screen of claim 2, furthercomprising detecting primary transducer failure by measuring theprojection screen vibrations.
 12. The method for reducing speckle on aprojection screen of claim 11, further comprising measuring projectionscreen vibrations with at least one accelerometer.
 13. The method forreducing speckle on a projection screen of claim 11, further comprisinglocating redundant transducers on the projection screen.
 14. The methodfor reducing speckle on a projection screen of claim 13, furthercomprising driving the redundant transducers only when a failure of atleast one primary transducer is detected.
 15. The method for reducingspeckle on a projection screen of claim 1, further comprising locatingvibrating elements behind masking to reduce acoustic transmission fromthe vibrating elements.
 16. A projection screen system comprising: aprojection screen; and at least one primary vibrating element attachedto the projection screen, wherein the vibrating element vibrates thescreen within a predetermined frequency spectrum, wherein thepredetermined frequency spectrum has power which is broadly dispersedwithin the predetermined frequency spectrum, further wherein vibratingthe screen mitigates the speckle to an acceptable level.
 17. Theprojection screen of claim 16, wherein the projection screen comprises ahigh elastic modulus substrate.
 18. The projection screen of claim 16,wherein the at least one primary vibrating element comprises at leastone primary transducer.
 19. The projection screen of claim 18, whereinthe at least one primary transducer comprises a voice coil.
 20. Theprojection screen of claim 16, wherein the predetermined frequencyspectrum is in the approximate range of 50-200 Hz.
 21. The projectionscreen of claim 16, wherein the acceptable level for speckle is lessthan approximately less than 15 percent contrast at approximatelyfifteen feet from the projection screen.
 22. The projection screen ofclaim 17, wherein the high elastic modulus substrate has an elasticmodulus of greater than approximately 0.4 GPa.
 23. The projection screenof claim 16, wherein the at least one primary vibrating element ismounted directly adjacent to the projection screen.
 24. The projectionscreen of claim 16, further comprising redundant vibrating elements inaddition to the at least one primary vibrating element, wherein theredundant vibrating elements are driven only when a failure of at leastone of the primary vibrating elements is detected.
 25. The projectionscreen of claim 16, further comprising masking located to dampen audibleacoustic transmission from the at least one primary vibrating element.26. The projection screen of claim 16, wherein the masking is located onthe front and the back of the projection screen.
 27. The projectionscreen of claim 25, wherein the masking further comprises noiseabsorbing material.